The goal ofthis application is to provide specialized training in animal taste psychophysics, a field which is indispensablle in linking neurobiological mechanisms of the gustatory system to behaviorally assessed taste function. To achieve this goal, experiments will be conducted using psychophysical procedures to assess the effects of pharmacological modulation of serotonin on taste-guided behavior in rats. Drugs that affect ingestive behavior are often assumed to do so by modulating the rewarding characteristics of the taste of foods and fluids. Understanding the mechanisms of action of these drugs is crucial to defining the role of the hedonic aspect of taste in eating behavior, which indisputably is contributing to this nation's growing problem with obesity. However, it is premature to conclude that a drug only affects hedonic components of taste without first assessing its effects on sensory-discriminative function. Serotonin is a ubiquitous neurotrasmitter that has actions in areas of the brain and periphery involved in taste and reward. Drugs that impinge on serotonergic transmission affect ingestion of food and fluid and impact taste perceptions in depressed and healthy humans. The extent to which this results from hedonic or discriminative aspects of taste has yet to be determined. The experiments in this proposal are designed to explicitly test the dose-related effect of an inhibitor and a facilitator of serotonin reuptake (and thus a functional agonist and antagonist, respectively) on performance in psychophysical tasks. These tasks assess concentration-dependent changes in the detection of, identification of, and hedonic responsiveness to taste stimuli. In a field advancing rapidly toward understanding the physiologic hardware of taste perception, scientists fluent in behavioral techniques are needed to link the growing body of information concerning the neurobiological, cellular, and molecular mechanisms of taste processing to its final common output - behavior. PUBLIC HEALTH RELEVANCE: The experiments in this proposal are designed to assess how drugs not only affect how "good" or "bad" something tastes, but also how strong it is and what it tastes like, independent of its rewarding or aversive characterisfics. These studies will help define how chemical signaling in the body affects taste-guided behavior (i.e., eating and drinking). This informafion may help clinicians understand and more effectively treat patients with eating disorders affected by the rewarding characteristics of taste (e.g., obesity) and psychiatric disorders in which taste percepfions are distorted (e.g., depression).